The present invention relates to optical lens systems utilized in medical endoscopes.
Medical endoscopes are utilized to view specific internal areas of the human body. Typically, endoscopes include a long, thin, rigid, or semi-rigid, optical cylinder affixed to a viewing mechanism. The cylinder is sufficiently narrow to be inserted through natural, or small, surgical body openings. When the endoscope is inserted and positioned for use, an image of the object being viewed is formed at an inserted end of the endoscope by an objective lens. The image passes through a series of relay lenses down the cylinder to an eye lens or video camera at a viewing end of the endoscope.
The relay lenses must be very narrow and are typically around 2.4 mm to 3.0 mm in diameter, and 20 mm to 30 mm long. Each relay lens is usually made of two or more elements and a pair of two relay lenses make up a set of relay lenses. Most endoscopes require two or more sets of relay lens pairs for proper operation. The number of sets depends on the length and specific requirements of a particular endoscope.
Additionally, unique optical characteristics of each relay lens require specific spacing distances between a pair of relay lenses within a set, and between sets of relay lens pairs within an endoscope. The required distances are maintained by hollow, cylindrical, interlens spacers.
Known relay lenses generally comprise one or two relatively thin end lenses affixed to a substantially thicker center lens. Where one end lens is affixed to a center lens the resulting relay lens is frequently referred to as a "doublet". And, where two end lenses are affixed to opposed ends of a center lens, the relay lens is referred to as a "triplet". Both doublets and triplets are shown in U.S. Pat. No. 4,575,195 to Hoogland.
Problems associated with known relay lenses include the high cost of accurately affixing the end lenses to the center lens. Typically, lenses are assembled within standard optical "V-blocks", but the thin end lens tend to be unstable unless mechanically supported within the "V-blocks" during cementing. The diameter-to-thickness ratio of most end lenses is roughly comparable to that of standard corrective contact lenses. The difficulty of affixing such end lenses is exacerbated in the manufacture of triplets because the end lenses have to be precisely aligned on the opposed ends of the center lens, whereby all three lenses share a common central axis.
An additional problem associated with known relay lenses is the requirement that the relay lenses and interlens spacers be inserted into the optical cylinder of the endoscope in a specific alignment and in a specific order. Frequently, during assembly of the endoscope, relay lenses are put in upside down, or in the wrong sequence. Also inter-lens spacers are often inserted in the wrong order. The error may not be detected until the endoscope is tested by an end user. Disassembly and extraction of the lenses and spacers is a difficult, time consuming and costly procedure.
Another problem of known relay lenses is the high cost of manufacture of the end and center lenses. Center lenses, in particular, require very delicate procedures. They are relatively long; extremely thin; typically made of glass; and therefore, crack and break easily. Additionally, precisely curved lens surfaces must be formed on each end surface of the center lens. Moreover, some relay lenses utilize different end lenses attached to the same center lens. Essentially, they require manufacture of three separate lenses for each relay lens.
Consequently, because of structural limitations, known relay lenses are difficult to fabricate due to the relatively short axial lengths of their end lenses; they require extreme care in assembly within an endoscope due to the varying alignment and space requirements of the relay lenses and inter-lens spacers; and, they are costly to manufacture due to the relatively long axial lengths of their center lenses and the need for multiple lens surfaces.
Accordingly, it is the general object of the present invention to provide an improved endoscope relay lens that overcomes the problems of the prior art.
It is a more specific object to provide an improved endoscope relay lens that has elements that facilitate assembly of the relay lens due to their relative sizes.
It is another object to provide an improved endoscope relay lens that facilitates alignment and spacing of the relay lenses within an endoscope.
It is yet another object to provide an improved endoscope relay lens that has elements that are substantially less expensive to manufacture than the elements of known relay lenses.
It is still another object to provide an improved endoscope relay lens that has optical performance characteristics that are substantially superior to the performance characteristics of known relay lenses.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.